1. Field of the Invention
The present invention relates to a method for producing a hydrogen-detection sensor, in addition to the sensor produced using this method.
The main application of the invention is in the field of thermoelectric solar power for the detection of the possible hydrogen produced as a result of the decomposition of the heat-carrying fluids used in this industry. The sensor developed is also recommended in applications which require the detection of small traces of hydrogen in a large variety of industrial environments.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Although in the bibliography, both scientific and of patents, a great variety of hydrogen detection methods has been reported based on processes that measure the changes in conductivity in oxide semiconductors such as ZnO, SnO2, TiO2, etc., generally activated using the presence of metal particles capable of dissociating the molecular hydrogen (e.g. Pt, Pd, etc.), an essential drawback thereof is its necessity of having to operate at high temperatures (above ambient), which, in addition to requiring localised heating systems, poses the danger of inducing explosions if the hydrogen to detect is in the air or mixed with oxygen.
As a result of these drawbacks, in the state of the art there are hydrogen detection sensors which work at ambient temperature and are based on principles of a colour change (chromophore sensors) which do not have electrical circuits inclined to generate sparks capable of producing gas ignition. A typical way of achieving said colour changes consists of mixing an easily reducible oxide such as WO3, MO3, ZnO, etc. and particles of metals such as Pt, Pd, etc., capable of dissociating the hydrogen molecule at low temperatures. This conceptual approach has been the object of various works and has been claimed in patents such as JP2007155650-A, JP2011021911-A. A very important condition for the operating capacity of this type of systems is that the oxide has a high porosity to promote a broad contact between the gas (hydrogen in this case) and the oxide in question. This high porosity also enables that the more expensive element of the system, the metal (Pt, Pd, etc.), can be dispersed in the form of small particles thus decreasing the overall quantity to be used. These conditions have obliged the devices of the state of the art to use the oxide in the form of powder, which involves various difficulties in their processing and fixing on substrates, also preventing the use of optical detection methods that require non-light dispersible materials.
Dealing with these difficulties, patent WO 2009133997 claims the development of a sensor in the form of thin layers using magnetron sputtering techniques where an oxide such as WO3 prepared in compact form is intercalated between a substrate and a continuous and compact layer of Pt—Pd also prepared using magnetron sputtering. This architecture enables that the oxide WO3 changes colour when the outer layer of Pt—Pd is exposed to hydrogen, although it may be problematic when regulating the magnitude of the change in colour which, given the difficulty of diffusion through a compact layer, it would only occur in the atomic layers of the WO3 in close contact with the metal layer.
In view of the above, the present invention proposes a new method for producing an H2 sensor with the aim of resolving the drawbacks of the H2 sensors existing in the state of the art.
The method disclosed in the present invention is a simple process which enables minimising costs, since it allows optimising the quantity of active metal necessary for producing the sensor, in addition to providing an H2 sensor with the following advantages:                It is capable of working at ambient temperature and up to around 550° C.        It allows the optical detection of H2 with the naked eye.        It is a reversible sensor which changes colour in the presence of H2 and returns to its normal state in the absence of said gas.        It is an accumulative sensor the colour of which increases with exposure to H2 gas, in addition to with the concentration of said gas.        